The present invention generally concerns building structures, and more specifically concerns a building structure made from a large extrusion of polymeric material which facilitates manufacture of the building structure while advantageously maintaining the appearance of conventional wood frame residential housing. The present invention further concerns a method and apparatus for manufacturing the building structure.
A number of building structures have been proposed for making low cost affordable housing. However, the known low cost building structures usually look "low cost" and lack aesthetic appeal making them unattractive to tenants. The known building structures can be made more attractive by customizing the building structure on site; however, on-site customization is not "low cost" since it requires use of skilled labor on site. Also, additional features facilitating on-site construction and/or customization of the building structure are desired. At the same time, improvements yielding greater mass production efficiencies are desired.
Some low cost structures use cement as the load bearing structural material. For example, in U.S. Pat. No. 2,691,291 (to Henderson) there are disclosed multiple precast concrete segments that can be assembled to form a building structure. However, prefabricated cement segments are cast, which is a batch-type process requiring multiple forms and consuming considerable time while the cement cures. Further, the segments are solid concrete making them heavy even if they are only a few feet long. For example, Henderson discloses that the segments must be made relatively short in length to avoid segments that are "too large or unwieldy" (see Henderson, column 1, lines 13 and 14). It is noted that the short length makes the on-site assembly tedious since not only must multiple pieces be carefully aligned, but also equipment for manipulating the heavy segments must be present on site. Still further, concrete is not always the material of choice. For example, concrete is thermally conductive, and thus has a poor energy efficiency making it less desirable in cold climates. Still further, precast and uncovered concrete tends to have a cold, "uninviting" appearance that is very different from conventional wood frame residential housing. This often makes the buildings unacceptable to tenants, unless substantial work is performed on site to customize the building. However, the on-site customization is costly, as noted above. Additionally, it is noted that it is very difficult to make on-site modifications and/or customizations in the cement structure, such as the addition of windows or doors since the walls and roof are solid concrete.
In U.S. Pat. No. 3,923,436 (to Lewis), there is disclosed an elongated building structure manufactured on site from foamed-in-place material. The load bearing material of the building structure is the foamed-in-place material which must be made strong enough to withstand the stresses and abuse encountered by a typical building. Lewis notes that it may be desirable to increase the durability and toughness of the exterior skin of the foamed-in-place material, and for this purpose Lewis discloses that surfacing material may optionally be added to the inside and/or outside of the foamed-in-place material (see column 3, lines 18.sup.+). However, even with the addition of the surfacing material, the foamed-in-place material forms substantially the entire load bearing portion of the building structure. Lewis does not suggest constructing a load bearing wall section having structurally stiff layers at the inner and outer surfaces which, from an engineering standpoint, is where the load bearing structure is most needed. Further, in Lewis there are no flanges on the surfacing material that facilitate finishing the building structure, nor are there any features on the surfacing material or on the foam material of the wall that facilitate installation onto a foundation. Also, it is noted that the foamed structure in Lewis is substantially limited to on-site fabrication since the foam has a poor tensile strength and may crush or break if impacted or bent, such as often happens during shipping. However, on-site fabrication is expensive, difficult to control, and does not take maximum advantage of mass production. Still further, even with the addition of surfacing material to the foamed-in-place material in Lewis, the long term durability of the building walls is potentially not as good as desired.
In regard to the apparatus and method disclosed in Lewis, Lewis teaches use of a machine including a foaming device and adjustable forms which can be used on site. However, such equipment tends to be cumbersome to use, expensive to ship, and requires skilled labor to safely operate. Further, the apparatus requires use of hazardous materials on site, such as isocyanide material in the case of polyurethane foam. Still further, it is noted that the apparatus is not productive during transport or setup, and further is subject to vandalism while on site, thus making the overall cost higher than may initially be apparent. As a practical matter, it is noted that the sidewalls of a foam structure made by the Lewis machine may tend to bulge or wander as the structure is being formed or as the foam is curing, thus leading to later complaints from tenants about the building quality. This is a difficult problem since the building is constructed on site where there is less than optimal quality control. Lewis also suggests that the machine can be used to manufacture a building structure including a floor (column 6, lines 62.sup.+). However, any such floor structure would require continuous support until the floor cured to a self-supporting state, which would be a slow and tedious process for foamed-in-place material or cement, and thus which is not conducive to mass production.
It is noted that the Lewis patent also discloses that cement can be used instead of foamed-in-place materials; however, this produces a building structure having limitations not unlike those disclosed in Henderson, which were discussed above.
Thus, a building structure and method and apparatus for manufacturing same solving the aforementioned problems are desired.